Research On Unmanned Aerial Vehicle Wireless Charging Technology Based On Three-Phase Asymmetric Coupling Magnetic Field

The Unmanned Aerial Vehicle(UAV),as an important detection equipment,which has been widely used in military investigation,civil detection,and so on.Limited by capacity and carrying capability,UAV can carry the small battery capacity and its work scope is limited,which have become one of the bottleneck restricting UAV further development.With its advantages of safety and reliability,no need to consume manpower,and so on,wireless charging technology is expected to be an effective means to solve the UAV charging problem and achieve the goal of UAV full automation.Therefore,a three-phase wireless charging system for UAV is designed from four aspects respectively in this paper,which are circuit design,magnetic coupler,misalignment tolerance capability improvement and closed-loop system realization.The three independent single-phase inverter circuits are selected as the three-phase inverter circuit and the primary three-phase coupling coils adopt three-phase independent connection mode,in order to balance and control the three-phase inverter output current.According to the requirement of output constant voltage source,the compensation structure of LCL-S is selected and the system working performance is analyzed.The circuit model of each part of the three-phase wireless charging system is established,and the steady-state mathematical description of each part of the system is obtained.The ranges of system inductance parameters are determined by using MATLAB software for 3D scanning within the ranges of system transmission power of50-120 W and system transmission efficiency greater than 70%.A circuit simulation is built in the PSpice software to analyze the system output characteristics and the working performance.the simulation results confirm the stability of the designed three-phase wireless charging system and the accuracy of the circuit model.A magnetic coupler based on three-phase asymmetric coupling magnetic field is proposed for the special limitations of small UAV internal space,weak carrying capability,limited landing accuracy and more internal precision equipment.The distribution of coupling magnetic field is analyzed by using ANSYS Maxwell software,and the structure of the three-phase asymmetric magnetic coupler is designed.The three-phase asymmetric magnetic circuit model of magnetic coupler is established,the mechanism of electric energy transmission is studied,and the mathematical description between the inductance parameters and geometry parameters of the magnetic coupler is obtained.According to the design index of circuit parameters and inductance parameters,the magnetic coupler geometry parameters are optimized by the parameter iteration method.Comparing the theoretical values of inductance parameters corresponding to the geometry parameters of the optimized magnetic coupler with the actual values measured by the LCR impedance analyzer,the maximum error is only 16.773%,the difference is small,which confirm the accuracy of the established magnetic circuit model and also indirectly illustrate the practicability of the proposed optimization method.To expand the UAV’s charging area,eliminate the charging blind area on the charging platform,the entire charging platform is covered with transmitting coils,which form the arrayed magnetic coupler.The misalignment tolerance capability of the single magnetic coupler under different misalignment conditions is studied,and the influence of misalignment on the system inductance parameters and power transmission capability is analyzed.Aiming at the problem of position detection in the arrayed magnetic coupler receiving coil,a detection method of the primary and secondary side communication is proposed,which control the switch tubes of each groups of transmitting coils in the wireless plane power supply network,and accurately open the three transmitting coils closest to the receiving coil,forming a group of single magnetic coupler to charge the UAV.The misalignment tolerance capability of the arrayed magnetic coupler under different misalignment conditions is studied and compared with the simulation results of the single magnetic coupler.The comparison results show that the arrayed magnetic coupler ensures that UAV can charge normally at any position of the charging platform and achieve the goal of UAV full automation.To verify the feasibility for the design in this paper,an experimental platform of UAV three-phase wireless charging system with power grade of 70 W is built,and the system performances under the condition of variable load and misalignment are analyzed.The open-loop simulation results show that the system can maintain the output constant voltage source characteristics well under the condition of variable load.The output power from constant current charging to constant voltage charging stage is more than 70 W,and the DC-DC efficiency is more than 70%,which meet the requirements of the design index.The fluctuation range of the rectified output voltage in the case of misalignment can meet the requirements of lithium battery charging.The closed-loop simulation results show that the built closed-loop system can realize the stage charging of lithium battery with constant current and constant voltage in the range of the lithium battery equivalent resistance change and allowable misalignment.